Epidemiological and virological factors determining dengue transmission in Sri Lanka during the COVID-19 pandemic

BackgroundWith the onset of the COVID-19 pandemic in early 2020 there was a drastic reduction in the number of dengue cases in Sri Lanka, with an increase towards the end of 2021. We sought to study the contribution of virological factors, human mobility, school closure and mosquito factors in affecting these changes in dengue transmission in Sri Lanka during this time. Methods and findingsTo understand the reasons for the differences in the dengue case numbers in 2020 to 2021 compared to previous years, we determined the association between the case numbers in Colombo (which has continuously reported the highest number of cases) with school closures, stringency index, changes in dengue virus (DENV) serotypes and vector densities. There was a 79.4% drop in dengue cases from 2019 to 2020 in Colombo. A significant negative correlation was seen with the number of cases and school closures (Spearmans r=-0.4732, p=<0.0001) and a negative correlation, which was not significant, between the stringency index and case numbers (Spearmans r= -0.3755 p=0.0587). There was no change in the circulating DENV serotypes with DENV2 remaining the most prevalent serotype by early 2022 (65%), similar to the frequencies observed by end of 2019. The Aedes aegypti premise and container indices showed positive but insignificant correlations with dengue case numbers (Spearman r= 0.8827, p=0.93). ConclusionsLockdown measures, especially school closures seemed to have had a significant impact on the number of dengue cases, while the vector indices had a limited effect.

Antibody and T-cell responses to a single dose of the AZD1222/Covishield vaccine in previously SARS-CoV-2 infected and naive health care workers in Sri Lanka

BackgroundIn order to determine the immunogenicity of a single dose of the AZD1222/Covishield vaccine in a real-world situation, we assessed the immunogenicity, in a large cohort of health care workers in Sri Lanka. MethodsSARS-CoV-2 antibodies was carried out in 607 naive and 26 previously infected health care workers (HCWs) 28 to 32 days following a single dose of the vaccine. Haemagglutination test (HAT) for antibodies to the receptor binding domain (RBD) of the wild type virus, B.1.1.7, B.1.351 and the surrogate neutralization assay (sVNT) was carried out in 69 naive and 26 previously infected individuals. Spike protein (pools S1 and S2) specific T cell responses were measured by ex vivo ELISpot IFN{gamma} assays in 76 individuals. Results92.9% of previously naive HCWs seroconverted to a single dose of the vaccine, irrespective of age and gender; and ACE2 blocking antibodies were detected in 67/69 (97.1%) previously naive vaccine recipients. Although high levels of antibodies were found to the RBD of the wild type virus, the titres for B.1.1.7 and B.1.351 were lower in previously naive HCWs. Ex vivo T cell responses were observed to S1 in 63.9% HCWs and S2 in 31.9%. The ACE2 blocking titres measured by the sVNT significantly increased (p<0.0001) from a median of 54.1 to 97.9 % of inhibition, in previously infected HCWs and antibodies to the RBD for the variants B.1.1.7 and B.1.351 also significantly increased. Discussiona single dose of the AZD1222/Covishield vaccine was shown to be highly immunogenic in previously naive individuals inducing antibody levels greater than following natural infection. In infected individuals, a single dose induced very high levels of ACE2 blocking antibodies and antibodies to RBDs of SARS-CoV-2 variants of concern. FundingWe are grateful to the World Health Organization, UK Medical Research Council and the Foreign and Commonwealth Office.

Annual risk of tuberculosis infection in Sri Lanka: a low prevalent country with a high BCG vaccination coverage in the South-East Asia Region

Introduction: Despite its simplicity, efficiency and reliability, Sri Lanka has notused the Annual Risk of Tuberculosis Infection (ARTI) to assess the prevalenceand efficiency of tuberculosis (TB) control. Hence, a national tuberculin surveywas conducted to estimate the ARTI.Materials and Methods: A school‑based, cross‑sectional tuberculin survey of4352 children aged 10 years irrespective of their BCG vaccination or scar statuswas conducted. The sample was selected from urban, rural and estate strata usingtwo‑stage cluster sampling technique. In the first stage, sectors representing threestrata were selected and, in the second stage, participants were selected from120 clusters. Using the mode of the tuberculin reaction sizes (15 mm) and themirror‑image technique, the prevalence and the ARTI were estimated.Results: The prevalence of TB estimated for urban, rural and estate sectors were13.9%, 2.2% and 2.3%, respectively. The national estimate of the prevalenceof TB was 4.2% (95% CI = 1.7-7.2%). ARTI for the urban, rural and estatesectors were 1.4%, 0.2% and 0.2%, respectively, and the national estimate was0.4% (95% CI = 0.2-0.7%). The estimated annual burden of newly infected orre‑infected TB cases with the potential of developing into the active disease(400/100 000 population) was nearly 10‑fold higher than the national new casedetection rate (48/100 000 population).Conclusion: The national estimate of ARTI was lower than the estimates for manydeveloping countries. The high‑estimated risk for the urban sector reflected theneed for intensified, sector‑specific focus on TB control activities. This underscoresthe need to strengthen case detection. Repeat surveys are essential to determinethe annual decline rate of infection.